Different instructors have different ways of teaching.
Many students just want to be able to ride like they see on TV, or fast like their friends. To cater to this some instructors begin by moving people through pretty quickly, moving up paces once they have basic control and balance. This means that pretty soon the person might be cantering. However, is this student really riding, or just a passenger on a horse that knows what to do?
Eventually, once a student has moved through enough the next step is to improve it, which I think is where a lot of people stop lessons.
Then some instructors take a more skill based approach, working on and achieving competence as you go along. Even at the walk there is a lot to be learned; asking for a frame, extended walks, collected walks, flexion, turns, leg yielding, stopping and turning with seat. Then at the trot all of those things, and sitting and rising, adjusting paces, 2 point, stirrupless riding. Then there is riding in an arena, and riding out and I think a lot of people do spend a lot of time at walk/trot. I know when riding, I spend a lot of time at walk and trot. I guess I just feel that until I achieve what I want at the trot, there is no way I'll achieve it at the canter because to me the trot is in a way the easiest pace to achieve things in.
So I don't know what level you should be at. I learned in the sort of "fast and imprecise" way, and spent years later having to learn everything else. I would have preferred to learn it all right in the first place. I think as long as each lesson you feel that you learn something, and that you have improved on things, then you're moving at a good speed.